Field of the Invention
The present invention generally relates to lighting devices, and more particularly to a lighting device applied to a back-lighting device of a transmitted type liquid crystal display device.
Recently, a display unit has widely been employed in wordprocessors, personal computers or the like together with improvements in the display capacity and lighting performance. Further, it has been required to provide thin and light display units applicable to notebook-type devices and workstations using a large-size display. Particularly, there has been considerable activity in the development of high-luminance color display units. Under these situations, it has been necessary to provide high-luminance, high-efficiency lighting devices.
An edge light type back-lighting device has been applied to a liquid crystal display device. In such a type of back-lighting device, light is incident to a side surface of a transparent light conducting plate. The incident light is propagated through the light conducting plate so that the light is totally reflected at an interface of the light conducting place. The light conducting plate has a slope at its center portion, and is provided with white ink portions. Hence, the condition for total reflection is broken and the light is emitted via a light-emitting surface.
FIG. 1 is a diagram of a conventional edge-light type lighting device 90, which includes two fluorescent tubes 81, a light conducting plate 82 made of a transparent resin, incident surfaces 82a of the light conducting plate 82, a back surface 82b of the light conducting plate 82 on which a diffusion reflection pattern is printed, a light-emitting surface 82c of the light conducting plate 82, a reflection sheet 83, an emission surface 84, reflection mirrors 85 respectively enclosing the fluorescent tubes 81, a linear prism 86, a transparent diffusion sheet 87 and an inner propagation light 88 and an emitted light 89.
As shown in FIG. 1, the fluorescent tubes 81 covered by the reflection mirrors 85 are arranged so that lights emitted therefrom enter into the incident surfaces 82a of the light conducting plate 82. The light conducting plate 82 has slopes from the incident surfaces 82a so that the light conducting plate 82 becomes thinner toward the center thereof from the incident surfaces 82a. These slopes of the light conducting plate 82 form the light-emitting surface 82c. The diffusion reflection pattern which has a weighted white-ink pattern is formed on the back surface 82b so that the printed area of the pattern is increased as the distances from the fluorescent tubes 81 increase. The reflection sheet 83 provided on the surface opposite to the back surfaces 82b functions to efficiently and effectively emit light scattered by the diffusion reflection pattern. The linear prism 86 is provided on the emission surfaces 84 of the light conducting plate 82 in order to effectively collect the emitted light 89 in the normal line direction. Further, the diffusion sheet 87 which prevents the diffusion reflection pattern from being seen from the outside of the lighting device is disposed on the emission side of the linear prism 86.
The diffused lights emitted from the fluorescent tubes 81 enters into the incident surfaces 82a of the light conducting plate 82 and are propagated through the light conducting plate 82 while the condition for total reflection is satisfied. The angle of the inner propagation light 88 becomes sharp by an angle "THgr" of the light-emitting surface 82c each time the inner propagation light 88 is totally reflected. When the angle of the inner propagation light 88 becomes greater than the critical angle, the light is emitted via the light-emitting surface 82c as the emitted light 89. The inner propagation light 88 totally reflected by the light-emitting surface 82c reaches the back surface 82b is emitted via the emission surface 84 because the diffusion reflection pattern breaks the condition for total reflection.
However, the prior art lighting device has the following disadvantages. All lights emitted from fluorescent tubes 81 are not emitted via the emission surface 84. Some light emitted from one of the fluorescent tubes 81 is propagated through the light conducting plate 82 and is returned to the associated reflection mirror 85. At this time, the returned light hits the reflection mirror 85 and loss of light occurs. Hence, the efficiency in use of light is not good. This problem may be reduced by means of the sloped light-emitting surface 82c of the light conducting plate 82. However, it has not been possible to obtain sufficient and satisfactory lighting performance.
The linear prism plate 86 disposed between the light conducting plate 82 and the diffusion sheet 87 contributes to a reduction in the above loss of light to enhance luminance in the normal line direction. However, an interference will occur unless the pitch of linear prisms of the linear prism plate 86 is optimally selected with respect to the pitch between electrodes arranged in rows and columns of a display panel. Hence, in practice, the diffusion sheet 87 having a high degree of diffusion is used or optimal pitches of the linear prisms are selected with respect to the respective electrode pitches. However, the luminance in the normal line direction is decreased as the degree of diffusion is increased. Further, dies for the respective pitches of the linear prisms must be prepared, which leads to an increase in the production cost.
It is a general object of the present invention to provide a lighting device in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a thin, light and efficient lighting device having a high uniform luminance distribution.
The above objects of the present invention are achieved by a lighting device comprising: a light source; a light conducting plate having an incident surface receiving light emitted from the light source, a back surface and a light-emitting surface; and a reflection member having a first portion facing the back surface, and a second portion located on a side opposite to a side of the light conducting plate on which the light source is located, the second portion being spaced apart from the light conducting plate so that light emitted from the light conducting plate is oriented toward an emission surface of the lighting device.
The above objects of the present invention are also achieved by a lighting device comprising: a light source; a light conducting plate having an incident surface receiving light emitted from the light source, a back surface and a light-emitting surface; and a reflection member having a first portion facing the back surface, and a second portion located on a side opposite to a side of the light conducting plate which the light source is located, the light conducting plate comprising a plurality of concave portions which are formed on the back surface and orient light emitted from the light conducting plate via the back surface toward an emission surface of the lighting device, a parameter related to the plurality of concave portions being weighted so that an even luminance distribution can be obtained on the emission surface.
The above objects of the present invention are also achieved by a lighting device comprising: a plurality of units located on a plane; the plurality of units respectively comprising: light sources; light conducting plates, each having an incident surface receiving light emitted from the light sources, a back surface, a light-emitting surface and an edge opposite to the incident surface; and a reflection member facing the back surfaces of the light conducting plate.
The above objects of the present invention are also achieved by a lighting device comprising: a plurality of units located; the plurality of units respectively comprising: light sources; light conducting plates, each having an incident surface receiving light emitted from the light sources, a back surface, a light-emitting surface and an edge opposite to the incident surface; a reflection member facing the back surfaces of the light conducting plate; light diffusing means, formed on the back surface of each of the light conducting plates, for diffusing light traveling in each of the light conducting plates in the vicinity of the incident surface more greatly than in other portions of each of the light conducting plates; a first linear prism plate partially allowing the lights emitted from the light conducting plates to pass through the first linear prism plate and partially reflecting the lights toward a space between the light conducting plates and the first linear prism plate; and a second linear prism plate collecting the lights from the first linear prism plate in a normal-line direction on the emission surface, wherein: the light conducting plates are arranged so that a space is defined by edges of the light conducting plates; and the light-emitting surface of each of the light conducting plates comprises an inclined surface which goes down toward the second portion of the reflection member.
Another object of the present invention is to provide a display device comprising any of the above-mentioned lighting device.
This object of the present invention is achieved by a display device comprising a display panel, a lighting device configured as mentioned above.